Telephone dial system



Jan. 12, 1932. F. s. IRVINE 1,840,364

TELEPHONE DIAL SYSTEM Filed Oct. 18, 1930 9 Sheets-Sheet l MEG/NA! /N VE N TOR F5. IRVINE 8y A TTORNEY 1932-. F. s. IRVINE 1,840,364

TELEPHONE DIAL SYSTEM Filed Oct. 18, 1930 9 Sheets-Sheet 2 FIG. 2

INVEN ro/ F. 5. IR VINE GMMM' A TTORNEY F. S. IRVINE Jan. 12, 1932.

TELEPHONE DIAL SYSTEM FiledOct. 18, 1930 9 Sheets-Sheet 3 F. S. IRVINE Jan. 12, 1932.

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lllllllllllllll INVENTOR F5. /RV//VE By 6.696712%- ATTORNEY Jan. 12, 1932.

F. s. IRViNE TELEPHONE DIAL SYSTEM Filed Oct. 18, 1930 9 Sheets-Sheet 5 Ill-II A TTORNEY INVENTOP FSJRI INE By Qf/ nuk Jan. 12, 1932. F. s. IRVINE TELEPHONE DIAL SYSTEM N a R MW m e O/ T my V T No A S I a W56 8 E Q 9 Y B O 3 m m Fl. 0 w ,m m vQM e 0 0 d l 6 ll. 1 II w x9 F. S. IRVINE Jan. 12, 1932.

TELEPHONE DIAL SYSTEM A TTORNE V Jan. 12, 1932.

F. s. IRVINE 1,840,364

TELEPHONE DIAL SYSTEM Filed Oct. 18, 1950 9 Sheets-Sheet 9 In nu UM] a n 2 3 U Q t E Q k a E k Ill l u 5 u [l'l i m t as I "3 ILD Q 9 as w k L: c Q o INVENTO/P By FSJRV/NE A TTORNEV Patented Jan. 12, 1932 UNITED STATES PATENT OFFICE FRANK S. IRVINE, F GREENLAWN, NEW YORK, ASSIGNOR TO BELL TELEPHONE LABORATORIES, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK' TELEPHONE DIAL SYSTEM Application filed- October 18, 1930. Serial No. 489,579.

This invention relates to automatic tele ceive dial impulses from the calling subscriber and to thereafter set the train of selectors which connect the calling line with the called line. When the sender has completed this function, the line finder, link and sender are disconnected from each other; the last two returning to normal while the line finder remains operated as a part of the talking-circuit of the establishedconnection. The

link,therefore, being essentially a connecting cir uit whose holding time is small compared to that of the line finder, is most efficiently used if, after completing one association between a calling line finder and a sender, is immediately taken into use again to establish, in succession, similar associations between other calling line finders and idle senders.

The determination of the most ellicient size of a link group for a given number of line finders cannot be established with any degree of accuracy by the method of dividing the holding time of a link into that of a line finder chiefly because, in actual practice, the holding time of a line finder is different for each call and also because the rate of incoming calls is not uniformly distributed over a time period. The relationship between the elficient size of a link group to a given number of line finders must, therefore,be determined from observations of actual trafiic conditions from which is ascertained the percentage of line finders calling for senders from a group of line finders in all stages of operation, including the idle condition. This percentage, again, while furnishing the basic index for the number of links, nevertheless the actual number of links used is slightly larger as determined. by an additional deviation figure which must. be added, based upon the index determined according to traflic studies, to care for variations from the average in conversation hold ing time and incoming call rate, consistentv with the grade of service the operating company expects to furnish its subscribers.

In a number of installations where links are used'and where such studies have been made, it has been found that the efiiciency curve of a, link groupv is parabolic in form when plotted against the number of line finders accessibleto the group. This indicates that the eiliciency of the link group increases sharply at first with an increase in the number of line finders to which the group has access and then in smaller and smaller increments as the number of line fmders greatly increases. In accordance with the present invention, therefore, it is proposed to take advantage of this relationship to increase the eiliciency of the linksby providing them with accessibility to larger groups of line finders, but not beyond the point where the number of line finders provided is disproportionally great to the percentage rise in efficiency of the link group. Specifically with panel systems it is proposed to increase the number of line finders from 80 to 200 and provide a link group which can efficiently serve the larger number of line finders.

lVhile the invention hereinafter disclosed relates, as already mentioned, to panel systems, it is understood that it is not so limited and can be modified for adaptation to other well-known types of apparatus used in the telephone art.

In accordance, with the invention, therefore, one specific embodiment of which is disclosed herein by way of illustration, this is accomplished inthe following improved manner: The subscribers lines in an oflice are divided into major groups suitable to the number which can be accommodated on a line finder frame or a group of line finder frames containing 160 line finders capable of handling the trafiic originated by the subscribers whose lines terminate on these frames. These groups are divided into smaller subgroups which are wired to the contacts of the finder banks, the subgroups being preferably limited to the number of superimposed contacts of a bank. It may further be considered that the line finder switches are provided with as many sets of brushes as there are contact banks inthe frame and each set ofbrushes consequently having access to the subgroup of subscribers'in the bank with which the brush in question can operatively cooperate. With the arrangement of tripping brushes used in line finder switches of this character, it is only necessary for the line finder to move a distance corresponding to a brush group of lines to seize and make contact with any calling line of the group. That is, when a subscriber initiates a call, the particular set of brushes of an idle line finder having access to the group containing his line, is tripped and moved over the terminals of the group in search of such a line. By dividing the total groups of lines into smalljbrush groups, the time required for finding a calling line is materially reduced. I11 order to further decrease thehunting time of a line finder switch the brush group of lines are subdivided into smaller equal groups which, for convenience, will be designated hereafter as the A and B subgroups.

Conforming with the subdivision of a brush group of lines into A and B subgroups,

.' the line finders serving the major group in a frame ora group of frames multiplied together are divided into groups designated as the 'A and B subgroups and containing an equal number of switches. In the embodiment of the invention herein described, it is assumed-that the numberof subscribers in a major group is such that 160 line finders will satisfactorily handle the volume of trafiic originated by the major group. This number of line finders is subdivided into two groups are all busy and vice versa.

Confining attention to the group of line finders normally serving the A subgroups of subscribers as first choice and remembering that the A and B subgroups are identical in this respect, the group of line finders serving the A subgroups of a major group of subscribers lines are provided with two allotters, each having control of a subgroup of40 line finders of the group of 80. These allotters are arranged to alternately start line finders in the respective subgroups to which they have access and the line finder switches so as signed have access to contact banks in which the calling subscribers lines appear as first choice, that is, in all the A subgroups. Each allotter comprises a self-stepping switch to' the contact banks of which are wired the start circuits of the line finders to which the particular allotter switch has access. .A relay, through whose contacts is extended the linefinder start circuit, is common to both allotters and is under the control of the line "finders allotted to both allotters, so that the start circuit is switched alternately from one allotter to the other as the line finders allotted to either allotter'are taken into use. In this manner the starting point for allotting a line finder in either subgroup of 40 is shifted with each call thereby equalizing the distribution of wear amongst the line finders of the group. A similar pair of allotters with a common relay is provided for the group of 80 line finders serving the B subgroup of subscribers of the major group.

The link circuit proper consists of two switch-elements,"a selector finder and a sender selector. It also has a sequence switch and a group of relays. As more particularly described hereinafter the selector finder con nects with a calling line finder while the sender selector connects with an idle sender; the two selectors becoming functionally related through the medium of the link relays and sequence switch so that circuits may be established between the sender and the line finder for the successful completion of the call.

The line'finders in the subgroups mentioned above are terminal-ended on panel banks with which the link selector finders operatively connect. Four multiple banks are used, two for each 100 line finders, giving the link group an accessible capacity of 200 line finders. The connection between a calling line finder and sender through the medium of the connecting link requires the use of 6 leads, so that the line finder is wired to 6 contacts on the panel banks, 3 contacts on one bank and 3 corresponding contacts on the second bank. The selector finder is provided with 4 sets of brushes each brush set having access to 100 terminals of the bank with which the brush set can cooperate. Since each line finder, appears on two banks two setsof brushes are tripped for each connection, either the lower two for connection to line finders wired to the lower banks, or the upper two for line finders wired to the two upper banks. A trip rod and trip magnet, individual to each selector finder is used and, when the trip magnet is normal, the trip rod trips. the two lower brush sets, while when the trip magnet is energized, the two upper brushes are tripped.

It is apparentthat before a calling sub- I use, to find the calling line finder and seize an idle sender. The selector finderof the link taken into use must, therefore, hunt for the calling line finder and since the terminals of such a line finder may be anywhere in a set of 100 terminal contact banks to which the selector finder has access, considerable delay may result if, sa the selector finder must travel over 100 terminals before connocting with the calling line finder. Under such circumstances there is danger that the subscriber will begin to dial before the sender is ready to receive the pulses. It is therefore desirable to make this hunting time, on the average, as short as possible.

To materially reduce this hunting time to approximately the time that it takes a line finder to find a calling line in the subgroup of lines at the line finder frame, it is proposed to divide each group of 100 line finders accessible to a pair of brushes of the link selector finder into five groups of 20 line finders each and to divide the selector finder choice, the third group of 20 as third choice,

the fourth group of 20 as fourth choice and the fifth group of 20 as last choice. A similar division is made of the 100 line finders V which terminate on the-two upper contact banks of tie selector finder frame. These groups are progressively slipped to the next section of the contact banks wherein appear 7 the selector finder switches associated with inent of one subgroup of 20 line finders is made in each section so that this progressive slipping permits each group of 20 line finders to be first choice in one of the five sections of the bank. Normally, therefore, when a call originates in one of the line finder frames of the major group and a line finder is taken into use, regardless of whether it belongs to the A or B subgroups of line finders, a link is chosen, if one is available, from the group which is first choice to the subgroup of line finders containing the selected line finder. The associated selector finder is located in that section of the contact banks where the subgroup of line finder terminals containing a line finder taken into use, appear as first choice. Should no link be available in the first choice groups of links, means are provided for switching to the second choice group. A similar operation takes place in switching to the next progressive choice should all the links of the irevious choices be busy. If a first choice link is chosen the associated selector finder wil then have to hunt only over a maximum of 20 terminals in order to locate the line finder taken into use by the calling subscriber. It possible, however, that during heavy traific when the links are busy, fifth choice links may be taken into use in which case the selector finder may have to hunt over a maximum of 100 terminals before locating the line finder associated with the calling subscribers line.

In general, the system functions in the following mauner: hen a subscriber in any of the subgroups ori inates a call, the line finder start circuit, which is connected through the contacts of the allotter common relay to either one of the two allotters controlling the group of 4.0 line finders serving the subgroups as first choice causes the allotment a. line finder by that allotter switch to which the start circuit is connected at the time. The line finder starts hunting for the calling line and when it moves oil normal, the common relay is either operated and locked or released depending upon which of the two allotters assigns the line finder, since the line finders connected to one of the allotters control the operation of this relay while the line finders of the second allotter control its release. This relay t-ransfers the start circuit to the alternate allotier so that a subsequent calling line will have a line finder assigned from the group of 20 line finders controlled by the alternate allotter. At the same time the allotted line finder grounds its hunting terminal on the arc of its associated allotter switch and causes the switch to advance to the terminals of other line finders and stop on the first one which tests idle.

As already mentioned the entire group of links accessible to 200 line finders is divided into subgroups, each of which is first choice to two groups of 20 line finders each served by one of a pair of allot-ters that is, a group of 20 on the two lower banks and a group of 20 on the two upper banks. The link subgroups are arranged by means of the well-known paddle start circuit to be switched successively from one group of line finders to another, so that a calling line finder is caused to be connected either to a. link of first choice, if one is available, or progressively to one in the second, third, fourth or fifth choices depending upon the busy or idle condition of the links in the subgroups of the prior choices. When a line finder is assigned and starts to hunt for the calling line, the paddle start circuit associated with the particular group of line finders in cooperation with the line finders taken into use, functions to select the first idle link in the subgroup controlled by the paddle start circuit which is normally the first choice subgroup of links. Should all the links in the subgroup be busy, a series circuit through the busy links of the subgroup operates two relays of the paddle start circuit and transfers the allotted line finder to the link subgroup of the next paddle start circuit. This operation of advancing from one subgroup of links to the next continues until anidle link in one of the subgroups is found idle and taken into use, whereupon the associated selector finder will proceed to hunt for the allotted line finder in the first, second, third, fourth or fifth section of the contact banks, depending upon the subgroup to which the link taken into use belongs.

Each link is provided with a relay which controls the trip magnet of the selector finder and the operation or the non-operation of this relay determines which of the pair of brushes of the selector finder is to be tripped. This determination is made by grounding the contact of a relay in each of the line finders appearing in the two upper banks, while the relays of the line finders appearing in the lower banks are ungrounded. When a linefinder is allotted and the relay containing the discriminating ground operates, a path is closed by way of the selected link which either results in the opera-Zion or non-operation of the relay in the link controlling the trip magnet of the selector finder depending upon whether the contacts of the line finder relay closin this path are grounded or not. The operation of the relay will cause the operation of the trip magnet which controls the rotation of the trip rod for tripping the two upper brush sets. if the relay does not operate, indicating that the allotted line finder is located inthe two lower banks, the trip magnet, of course, is not operated and, according to the mechanical structure of the tripping mechanism, the two lower brush sets are tripped. 7

When a link is selected and connection is made with the allotted line finder, the link s quence switch is advanced to the next position where the link is set in operation for hunting and seizing an idle sender by a Wellknown rneans. With the link attached to both the calling line finder and an idle sender, the sequence switch is advanced to a cutthrough position where paths are established through the link between the line finder and the sender for the operation and control of the various circuits necessary for the sender to properly guide the selectors to the called subscribers line.

When this function is completed circuits are closed in the link from the line finder which serve to disconnect the selector finder switch from the terminals of the line finder and cause it to return to normal. Similarly circuits are closed in the link from the sender, which causes the link to open the connecting leads between the link and the sender. The link circuit is thereafter restored to normal by advancing its sequence switch to a. normal position after whichv it is advanced again to its reassignment position.

. The above and other features of the inven tion will be apparent'from a consideration of the following description in connection with the drawings and appended claims.

Referring to the drawings:

Fig. 1 shows one of a group of subscribers lines together with a tripping circuit common to the group of lines;

' Fig. 2 shows a start circuit serving a pluality of tripping circuits;

Fig. 3 shows two link allotters together with the cooperating parts of the links of two groups of link circuits controlled by said allotters;

F 1 shows a line finder-district selector circuit for extending the line of Fig. 2 to succeeding selectors;

Fig. 5 shows oneof a plurality of link circuits controlled by the allotters of Fig. 3 and havingaccess to the line finder-district selector circuit of Fig. 4;

Fig. 6 shows a portion of a sender circuit adapted to be selected bythe link circuit of Fig. 5;

Figs. 7 and 8, taken together and arranged in accordance with Fig. 11 show in a diagrammatic manner, the relationship between the arrangement and distribution of. line finder circuits on a link finder frame, the cooperating link finders thereat and the co operating link circuits;

Fig. 9 shows schematically the successive switching stages of one type of connection for which the present invention is adapted to operate in building up a telephone connection to a wanted subscriber;

Fig. 10 shows the manner in which Figs. 1 to 6 inclusive and Fig. 9 of the drawings should be arranged to disclose the invention completely; and I Fig. 11 shows the manner in which Figs. 7 and 8 should be arranged.

It is to be noted that Fig. 6 is a skeletoniaation of the sender shown in U. S. Patent 1,589,402 granted to O. H. Kopp, June 22, i

of relay 103 to ground at the outer contacts of relay 101.

=The operation of relay 103 closes a circuit from battery, resistance 105 to ground at the right outer contacts of relay 103. This circuit is in shunt to the winding of relay 106, which relay serves the second subgroup of lines of the group to which line relay 100 belongs, thus preventing the extension of a call from that subgroup, while the tripping circuit is I in use with line 100. The operation of relay 103 also closes a circuit from battery through the winding of relay 200, conductor 133, left outer contacts of relay 107, left outermost contacts of relay 103 to ground.

Relay 200 operates and connects ground over its contacts and conductor 132 to the right inner armature of relay 107. WVhen re lay 107 operates, as described hereinafter, it looks to ground through its right winding andremains locked as long as relay 200 remains operated. With relay 107 operated, the operating circuit of relay 108 remains open and hence any other incoming calls in this group must await the release of relay 107 before they can be extended. Since relayY 200-operates assoon as relay 103 or relay 106 operates, it will remain operated as long as a call awaits in any subgroup served by the start circuit of Fig. 2. The relay of each trip circuit corresponding to relay 107 operates as each call is served and locks to the contacts of relay 200. When all waiting calls have been served the circuit of relay 200 is opened and that relay releases, releasing the relay 107 to permit the extension of other calls. Since the circuit of relay 200 is extended over the back contacts of relay 107, should simultaneous calls exist in all the groups served by the start circuit of Fig.2, when one call has been served in each group and relay 107 of the'last trip circuit has been operated, no circuit would exist for holding relay 200 operated and that relay would release, permitting the relays 107 to release and close over their back contacts circuits for again operating relay 200 should additional calls await attention.

In addition, relay 103 closes a circuit from battery, over the back contacts of relay 201,

conductor 130, right winding of trip relay 108, left inner contacts of relay 107, left in nermostcontacts ofrelay 103, right outer contacts ofrelay109 toground. Relay 108 0perates in this circuit and eloses a locking circuit-for itself from ground. right inner contacts of relay 109,-left winding and left innercontacts ofrelay 108 over the left innerbac-k contacts of the trip relays of the other groups of lines, conductor 129, right winding of start relay 201 to battery. Relay 201 operates in this circuit. A circuit is now closed for relay 110 extending frombattery through the winding of relay 110, right inn-er contacts ofrelay 108, conductor 128 to ground on the right outer contacts of relay 201. Relay 110 locks in a circuit to ground at the outer contacts of relay 109. Relay 108, together with relay 103, prepares a circuit from ground on the left contacts of relay 110, left outer contacts of relay 108, right inner contacts of relay 103, conductor 131, left middle back contacts of relay 202, left outer, back contacts of relay 203, conductor 206, bottom front contacts of relay 300, which relay may be operated as more fully described hereinafter, brush 314 and associated contact of distributor switch 311, conductor 303, winding of relay 400 to battery. Relay 400 operates and performs functions hereinafter described.

The operation of relay 108 also closes a circuit from ground over its right outer contacts, conductor 134 through the winding of trip magnet 401 serving the group in which line 100 appears in the line finder frame, to battery. Relay 110, upon energizing, closes a circuit from battery through the left windin of relay 109, left winding of relay 107, le contacts of relay 110 to ground. Relay 107 operates and locks through its right winding and right inner contacts, conductor 132 to ground on the contacts of relay 200.

The operation of relay 400 closes a. circuit from battery through the winding of updrive magnet 402, top inner contacts of relay 400, right contacts of cam 403, bottom outer front contacts of relay 400 to ground. Under the control of up-drive magnet 402, the line finder shaft is moved upwards. Due to the operation of the trip magnet 401, the set of brushes serving the group of lines to which line 100 belongs is tripped. Relay 400, on operating, also closes a circuit from ground on its bottom front contacts, right lower contact and cam 465, cam 468 and left upper contact thereof, top winding of relay 452 to battery. Relay 452, operates in this circuit but performs no useful function at this time. hen the line finder shaft leaves the tripping zone a circuit is closed from ground over brush 404 through commutator segment 405, right contacts of cam 406, conductor 407, left outer normal contacts of key 204, right inner contacts and right winding of relay 201 to battery. Belay 201 is held operated in this circuit but the circuit through the locking winding of relay 108 is shunted and this relay releases, in turn releasing trip magnet 401. As soon as brush 404 leaves commutator segment 405 the circuit of relay 201 is opened and this relay releases, again connecting battery to the operating winding of relay 108 and the corresponding relays of other trip circuits so that subsequent calls may be served.

As soon as the elevator shaft moves ofinormal relay 400 closes a locking circuit for itself over its bottom inner front contacts, left contacts of cam 408, back contacts of relay 409, commutator segment 410, brush 413 tor 207, right middle back contacts of relay 415 to ground on the bottom outer front contacts of relay 400. Relay 203 operates in this 7 circuit and removes ground from conductor 206, thereby preventing the starting of an other line finder until the brushes are tripped. Relay 203 looks in a circuit from battery over the left outer contacts of relay 205, left winding and left outer front contacts of relay 203, leftback contacts of relay 202, conductor 131, right inner contacts of relay 103, left outer contacts of relay 108, left contacts. of relay 110 to ground. The operation of relay 203 also closes a locking circuit for relay 201 from battery, left front contacts and left winding of relay 201, right inner contacts of relay 203 to ground. The circuits just traced are established before relay 108 is released by the shunting action of commutator segment 405. As soon, however, as relay 108 deeuergizes, it opens the locking circuit of relay 203 restoring the start circuit to a condition to serve sub- 3 tacts of jack 419, right outer contacts of relay 415, contacts of cam 416 to ground. Relay 415 closes ground on its left outer contacts, conductor 420, terminal on the arc of distributor switch 311 contacting with brush 306, winding of relay 300 to ground, resistance 309 to battery. Relay415 also closes another circuit from ground on another of its left outer contacts, conductor 424, terminal on are of distributor switch 311 contacting with brush 315, interrupter contacts of distributor magnet switch 311 to battery, Switch 311 operates and advances its associated switch brushes 314, 315 and 306 to the next set of contacts on the distributor switch arcs. Prior to the stepping of switch 311 to the succeeding terminals of the arcs, however, relay 300, which so far has been assumed, to be'locked to ground over its top contacts, releases by virtue of the ground on conductor 424 previously traced, shunting the locking batteryj through. resistance 309. The operating and releasing characteristics of relay 300 are such as to make it both fast operate and fast release compared to the time "i of operation of each of the distributor l switches 311 and 302 so that relay 300 always operates or releases before either distributor switch operates. The release of relay 300 transfers the start conductor 206 over its bot tom back contacts tothe arc of the distributor switch 302 associated with brushes 301, 310 and 312 and controlling thedistribution of another group of line finders having access to the same group of subscribers lines, as more clearly explained hereinafter. Should another call now be initiated by a subscriber belonging to the group having access to start conductor 206 then the start ground on this conductor will close a circuit for relay 400 in the line finder circuit of the second group of line finders controlled by distributor switch 302 and connected to the terminals of the are on which the brushes of said switch 302 are standing but which line finder is not shown in the drawings. When relay 415 of this other line finder operates as a result of the associated line finder shaft moving upwards and has made contact with its associated commutator segment 411, a ground is connected to conductor 307 in the same manner as ground was connected to conductor 420 by relay 415 of the previous line finder under description. The ground on conductor 307 closes a circuit path by way of brush 312 through the winding of relay 300, resistance 309 to battery operating thereby relay 300. At the same time, another ground on conductor 325, connected thereto by an operated contact of this other relay 415 closes a circuit by way of brush 310, and associated contact on the arc, interrupter con tacts of switch 302, winding of switch magnet 302 to battery. Switch 302 operates and advances brushes'301, 310 and 312 to the succeeding set of arc contacts connected with an idle line finder of the group. Conductor 206 is now transferred back to the contacts of the first distributor switch 311 by way of the bottom front contacts of relay 300. In this manner the allotment of line finders is alternated bet-ween the two groups of line finders controlled by each of the two distributor switches respectively, thereby reducing wear on line finders ordinarily first in preference and distributing the calling load evenly among all the line finders having accessibility to the group of subscribers on the line finder banks with which the line finders of both groups shown in Fig. 3 cooperate.

When all the line finders of both groups are taken into use a chain circuit is completed throughthe right'innermost contacts of all the relays 415 beginningwith a ground on the contacts of relay 415 of the first line finder in one of the two groups, through each of the chain of contacts on other relays 415 in series of the group, conductor 423, through the series chain of the second group of line finders, conductor 322, winding of relay'208 to battery. Relay 208 operates and closes a circuit from battery "through the left winding of relay 202, right'back contacts of relay 203, left contacts of relay 208 to ground. Relay 202 operates, disconnects conductor 131 from conductor 206 and transfers conductor 131 over the left back contacts of relay 209, right outer back contacts of relay 210 to conductor 211 connecting with two other groups of line finder circuits second in preference to the group of subscribers having the two groups of line finders shown in Fig. 3as first preference. 'lVhen, now, the allotted line finder in one of these two other groups is started, relay 210 is operated in a circuit from ground over conductor 212 corresponding to conductor 207, left winding of relay 210, left inner back contacts of relay 213 to battery. Relay 210 closes a locking circuit for relay 202 from battery through the right winding and right contacts of relay 202, left inner front contacts ofrelay 210 to ground, preventing the release of relay 202 should a line finder circuit in the first two groups become free before the callingline has been found. Similarly, as all the line finder circuits in the latter two groups become busy, ground through all the line finder circuits in a chain through the contacts of their respective relay 415, conductor 214 will cause the operation of relay2-15 which will, in turn, operaterelay 209, disconnect conductor 127 from conductor 211 and transfer it to conductor 206 leading to the first two groups of line finders.

If for any reason a line finder fails to start within a predetermined time a circuit will be completed from ground on the left contacts of relay 110, left outer front contacts of relay 108, right inner contacts of relay 103, conductor 131, left inner back contacts of relay-202, left inner back contacts of relay 203, contacts of interrupter 216, left winding of relay 217 to battery. Relay 217 operates when the interrupter 216, closes its lower contacts and looks through its left inner contacts to the above traced circuit independent of the interrupter contacts. After an interval, when interrupter 216 closes its upper contacts, the above traced circuit is extended over top the interrupter contacts, left outer contacts of relay 217, right winding of relay 205, left back contacts of relay 213 to battery. Relay 205 operates and locks in a circuit from battery through its left inner front contacts and left winding of re lay 205, key 220 to ground. The operation of relay 205 closes a circuit from battery through the left winding of relay 202, right outer contacts of relay 203, right inner contacts of relay 205 to ground, transferring calls from the first two groups of first pref erence to the second two groups of line finder circuits of second preference. ircuits are also closed for lamp 218 at the start cir cuit frame and lamp 219 at the trouble desk.

The operation of the link circuit, will now be described. The links are assigned one at a time after the line finders are taken into use in the manner previously described, position 2 of their respective sequence switches being the position in which all the links of the group except one are resting when awaiting an assignment. In order to show clearly how the assignment takes place consideration is directed to Figs. 3 and 5, the latter figure disclosing in detail all the elements of the link circuit except such parts as cooperate with the distributor start circuit shown in Fig. 3 wherein such parts of the link circuit of the two groups of links cooperating with the corresponding two groups of line finders are shown. Referring to Fig. 3, when all the links are normal, that is, in position 2 and no call is initiated in the group of subscribers having accessibility to line finders controlling the start conductor 206, a chain circuit is closed from ground though the contacts of cam 321 of each link, beginning with the last in the group, cam 324 and contact thereof of the first link, cam 305 of the first link and top contact thereof, conductor 308, magnet 509 to battery. Magnet 509 operates and advances the sequence switch of the first link from position 2 to position 3. The remaining links of the group now remain in their respective positions, that the first link In position 3 and the others in position 2 and the link which is in position 3 will be the one first to be assigned when a call is initiated over conductor 206. hen the call is initiated as already described and a line finder is taken into use in the group associated with distributor switch 311 and relay 415 operated in the assigned line finder as already described, a circuit is closed from ground on the left contacts of cam 426, top middle contacts of relay 421, left inner front contacts of relay 415, left winding of relay 417, conductor 328, left back contacts of relay 327, conductor 329, top inner back contacts of relay 320 to battery. Relay 417 operates and closes a holding circuit from ground through its right winding and right front contacts, conductor 432, left outer back contacts of relay 316, winding of relay 320 to battery. Relay 320 operates in series with the locking winding of relay 417, disconnects the operating battery from the left winding of relay 417 and establishes a locking circuit for itself over its bottom inner contacts, conductor 304 extending to the left lower and right top contacts of cam 542 of the assigned link when the said link advances to position 4 as described hereinafter. Relay also connects ground over its bottom outer contacts to the bottom contacts of relay 323 and thereby closes a circuit for relay 503 of the allotted link from ground on the bottom outer contacts of relay 320, bottom contacts of relay 323 through cam 343 and lower contacts thereof of all the links in the group which are in position 2 and the left lower and right upper contacts of cam 343 of the assigned 1121K in position 3, conductor 508, top outer make contacts of jack 506, bottom winding of relay 503 to battery. Relay 503 operates in this circuit and, through its bottom front contacts, connects ground to conductor 507, cam 332 and contacts thereof of the assigned link, conductor e30, normally made contacts and winding of relay 323 to battery thereby causing relay 323 to operate. Relay 323 looks over its top make contacts to ground on the bottom outer contacts of relay 320 and, at its oottom contact-s, opens the operating circuit of relay 503. Relay 503, however, does not release when its operating circuit is opened because, when it operates, it closes a circuit for sequence switch magnet 509 from ground on its top outer front contacts, right upper and left lower contacts of cam 511, winding of'magnetc509 to battery, advancing the sequence switch to position 4. In this position the top winding relay 503 is connected over its top inner contacts, right upper and left lower contacts of cam 514, bottom middle contacts of jack 506, brush 510 of the link finder shaft which cooperates with the link finder banks on which the line finders are terminals-ended. Brush 510 makes contact with the test terminals of the line finders, and all the line finder circuits QX- cept the one which has been allotted and awaiting connection with alink have ground connected to their respective test terminal over conductor 449, top inner contacts of jack 419, right upper and left lower contacts of cam 427 to the bottom outer contacts of relay 400. N ow any line finder is either in position 1 with relay 400 normal or with relay 400 operated, or it may be anywhere from position 2 to 13 in a condition of service with relay 400 either up or down. If the line finder is normal, that is, in position 1 and relay 400 is also normal, the path above traced connects ground to the corresponding test terminal associated with conductor 449 and holds relay 503 locked when the link tests the line finder in its hunt for the assigned line finder. If relay 400 is operated and the switch is in position 1, then the line finder is in an allottedcondition whereupon ground is not connected to conductor 449 and when the link tests the line finder there is no holding circuit for relay 503 and this relay releases. If, on the other hand, the line finder is busy and the switch has passed position 1, then ground from the left upper contact of earn 427 is connected to conductor 449 thereby again supplying a ground on the associated test terminal on the link finder bank. Moreover the advance of sequence switch 509 to position 4 and the consequent upward movement of the link finder'shaft to where brush 505 engages commutator segment 504, as more clearly 6X- plained hereinafter, provides a holding ground for relay 320 from gr ui on brush 505, commutator segment 504, right upper and left lower contacts of ca'm'542, conductor 304, bottom inner contacts'of relay 320 to battery. Relay 320 remains locked and, in turn, keeps relay 323 locked by ground on its bottom outer contacts. Should, now, another line finder be taken into use by distributor switch 311, starting ground for assigning another link over the bottom back contacts of relay 323 will not be available to start the second link until the previous link assigned has hunted and found the calling line finder, which event takes place in position 4 of the first link. lVhen the link has advanced out of position 4, the locking circuit of relay 320 is opened, thereby causing this relay to release and, in turn, releases relay 323 which, over its bottom contacts,

reestablishes the start ground over the link conductor 508 of the next link of the group inposition 3.

' When relay 320 operates it connects ground over its top outer front contacts, right back contacts of relay 327, conductor 430, left outer contacts of relay 417, bottom winding of relay 421 to battery. Relay 421 is not marginal with respect to its bottom winding and when the circuit just traced is closed, it operates and looks over its top winding and top inner contacts, left upper contacts and cam 443, cam 426 to ground. Relay 421 by its operation opens its top middle contacts controlling the operating circuit of relay 417 previously described, leaving relay 417 looked through its right winding in series with the winding of relay 320 during the interval between the assignment of the link and the connection of ground to conductor 304 by the assigned link, at which time the locking winding of relay 417 is shunted and the relay releases.

Should it come to pass that another link finder of a link in the group controlled by one distributor switch is taken into use during the interval when an assigned link is hunting the line finder which caused its assignment, the fact that relay 320 operated prevents the operation of relay 417 of the subsequently allotted line finder, since the operating battery for all relays 417 of the group controlled by one distributor switch is supplied through the top inner back contacts of relay 320. An assignment of another link, therefore, is delayed until such a time when the previously assigned link has been allotted to and made connection with the line finder which caused its assignment. When this happens, the sequence switch of the assigned link is advanced to position 5, as more fully explained hereinafter. Relay 320 is released and the operatingbattery to the winding of relays 417 of the group of line finders is reconnected to conductor 328, whereupon relay'417 of the awaiting but allotted line finder will then operate and lock in the manner described and, by reoperation of relay 320, cause the assignment of a link for its use.

' preference of the series lockout circuit and for assignment is advanced to position a. TlllS isaccoinphshed by a circuit over conductor 333, right lower contact and cam 305 consequently the operating circuit of relay 320 in series with it. In this manner an accumulation of allotted line finders have links assigned to thenione at a time.

Since the assigned link has advanced to position4, and recalling that all other idle links inthe. group are in the awaiting assignment' position 2, the-link next in succession of the link in position 4, cam 324 and left contact thereof, right contact and cam of the next link insuccession, cam 308 and uppercontact thereof to conductor 308 of that link to the associated switch magnet 509 which, whena line finder is taken into use causes the subsequent advance of the link switch to position' l as already described.

'lVhenJall the links of the group are thus made busy a chain circuit is closed from ground on the top outer back contacts of relay 320, contacts of cam 331 of each link, left windingof relay 316 to battery. Relay 310 operates and closes an obvious circuit for relay 327 which also operates. The operation ofthese two relays causes the transfer, over their front contacts, of the link start conductors-to the nextx'group of links having accessibility to the same line finder frame as explained more fully below. Relay 316 is provided with a rightlockingwinding to guard against the release of relays 316 and 327 when a line finder is taken into use and,

at the same time, a link becomes available in 415, top middle contacts of relay 421, left contactsof cam 426 to ground. Relay 316 is thus prevented from releasing and is held until the allotted line finder has been advanced out of position 1, which eventsucceeds the assignment of a link for that line finderfrom the next succeeding link group having an idle link to which the operated relays 316 and 327 have advanced the assigning conductors. A link will thus be assigned from the succeeding group even though a link in the previous group has become idle in the meanwhile.

Figs. 7 and 8 show the relationship, in a.

similar start circuits in Fig. 3. Figs. 7 and- 8, when considered in connection with Fig. 3, show clearly the manner in which the links are assigned and also the manner in which 555 the line. finder link start conductors are advanced from one group of links to another when all the links of the preceding group are busy.

of the link finder banks of the frame are represented by 701, 702 and. 703 and the line finder subgroups by the designationsCl-C2, D1D2, H3H4, K3-K4, etc. The letter designation indicates the line finder subgroup while the numerical sufiix therewith indicates the bank in which the group appears. Since each subgroup appears in either the two lower banks or the two upper ones, the

letter designation is the same for each pair of banks. Y

8 shows the manner in which the links, the link finders of the respective sections, and the link start circuits are inter-related. Each of the five sections of the link finder frame has its own group of links and each group .of links has two switching relays, namely relays 316 and 327, for transferring a calling line finder to the succeeding group of links. It will be noted, also, that the line finder subgroups associated with a group of links appear as first choice in that section of the link finder frame where the link finder shafts of corresponding link groups are located. Thus, line finder subgroups C1-C2, H3H4 are first choice to the link group having accessibility to section 701; the former subgroup being located in the two lower banks and the latter is located in the two upper banks. Similarly, line finder subgroups G1G2 and N3N4 are first choice to the link group having accessibility to section 702. It follows that since conductor 206 is the point of access connected through relay 300 toeither of these four subgroups of line finders, the subscriberv group on the line finder frame must have these four groups of line finders as first choice also; With such an arrangement, whenever a start ground is connected to conductor 206 it makes no difference from In Fig. 7 three of the five vertical sections;

which subgroupa line finder is chosen. lThe link associated with such line finder subgroup will be one for which the particular line finder group is first choice in the section of the link finder frame where the link finder of the assigned link appears. For example, referring to Figs. 7 and 8, assume that relay '300 is locked by the operation of a previous allotment, a subsequent call from the same group of subscribers will ground conductor 206 and, by means of the circuit operations already described, the ground on conductor 206 will be extended by way of brush 314 of switch 311 to a line finder in either group C1C2 or H3-H4. If the line finder allotted belongs togroup (ll-02, it will be .terminal-ended on the two lower banks of the link finder frame; otherwise, it will belong to group H3H4 and is terminal-ended on the two upper banks. When a line finder is assigned in the manner described ground will be connected to brush 306, relay 300 is re leased and switch 311 is advanced to the terminals of the next idle line finder of either group G1C2 or H3H4. By operations already'described, relay 320 in the associated link start circuit connects ground to start conductor 505 and causes the assignment of the first link which is in position 3 of the group. It will be observed that these links appearin section 701 where the line finder subgroups -Cl''C2 and H3H4 appear as first choice. +011 the other hand, if relay 300 is normal as a result of a previous allotment the start ground on conductor 206 and coming from the same group of subscribers as those which are accessible to line finder group's C1C2 and H3-H l, is connected to the link brush 301 of the distributing switch 302 therebycausing the allotment of a line finder in either subgroup Gl G'Q appearing in the two lower banks of section 7 02 or group N3 N4 appearing in the two upper banks of this section. Both of these two groups are first choice to a group of links and by an inspection of Figs. 7 and 8 it is apparent that this group of links is the one operatively associated with the line finder subgroups G1G2 and N3+N4. In the same manner it can be shown that the subscribers group associated with another starting conductor like conductor 206 andcooperating with a pair of distr butor switcheslike 302 and 311 are similarly associated with line finder subgroups which are accessible to the said subscribers group and which appear in such sections of the link finder frame as to be first choice to groupscooperating with the said sections. 3

WVhenall the links of a group have been assigned, that is, when the sequence switch of each link is in anyposition between 1 and 1, a chain circuit is closed from the bottom outer back contacts of relay 320through cam 331and contacts thereof of-each link switch,

left winding of relay 316 to battery as already described. Relay 316 operates relay 327. When, now, another call is initiated and a line finder is allotted fromeither group ClC2 or H3H4t, and it'is assumed that the link group cooperating with the section where they appear as first choice is busy, relays 316 and 327 transfer the link start conductors to the next succeeding group of links if relays 316 and 327 of the said next succeeding link start circuit are not operated; otherwise to the link group next in succession. WVith the selection of a link, from the next link group, that is, from the group cooperating with section 702, it will be observed that the line finders of the two sub- 2 groups G1-C2 and H3-H4 are not first choice in this section but second choice, so that when the link shaft moves upwards it will have to'travel over the first subgroup without hunting for the alloted line'finder and into the second group, either in the lower banks or the two upper ones to locate the allotted line finder. In the same way if, at the time that the links of section 701 are busy those of the section 702 are likewise busy and a call originates in a subscribers group having access to line finder subgroups C1 C2 or H3H4, relays 327 and 316 of both link groups being operated, the calling line finder may be connected to a link in section 703 where line finder subgroups C1C2 and H3H4 are third choice, in which case the line finder of the allotted link will have to travel over the two lower groups and hunt in the third group to find the calling line finder. In the same manner a calling line finder may be advanced to the two remaining link groups of the frame, which are not shown in the drawings, wherein the preference is still more remote, that is, subgroups C1C2 and H3H4t will be fourth preference in the fourth section and fifth preference in the fifth section. v

It is thus seen that when a link group of a section becomes busy, an allotted line finder which is first choice in that section is successively transferred to link groups of other sections to have assigned therefrom an idle link of the link group in that section but for which the calling line finder group is of a more remote preference. 7

Referring once again to Figs.'7 and 8, taken in connection with Figs. 3 and 4, and recalling that the line finder" is terminalend-ed on contact banks of the well-known panel type cooperating with the moving selectors of the same type wherein a set of brushes is provided for cooperation with each bank, it is evident that when a link is chosen for connecting an allotted linefinder with a sender through the medium of the link, such a connection must take place through two brush sets on the link finder shaft each Of Which is adaptedto engage the controlled in the, welleknown .inanner and adapted to app'ea for a-call no trippingmagnet operat1on is "required :for engaging; the terminals of the three .termi'nalsof theline .finder in; each of u the two banks wherethe line finder is terminail-ended. Since, in the present embodiment of the invention, there are four banks mall to alink finder rrame each link finder shaft is provided'with a tripping rod mechanism by the operation of a trip magnet isets cooperating with the two lower banks of section 701 and trip fingers 710 and 711 which will.-=trip the brush sets cooperating with the two upper banks, of section'701.

Now the tripping rod mechanism is so arranged that ,whenlthe trip magnet is not operated, the triprod 1s lnsuch a position that trip fingers 7 06 and 708 trip the two lower brushsets and when the trip magnet is operated, the trip fingers 7 06 and I708 arecieared out of the tripping Zone, and the two upper trip fingers 710and711 are-rotated into the tripping positionfortrippingthesaid two upper brush se'ts.;-1: Normally, therefore, when a line finder 1g, in thetwo. lower ban is allotted "allotted line finder as the two lower brush sets will he tripped. by the normal setting .of the tr1p-rod.-'rHowever, when a line finder .which appears: in the two upper banks is taken: into use'th-e trip. magnet of tne'associated line finder shaft of the link must be operatediin order to set the two upper pairs of brushes for connection be tween the cal in line finder and tlie' ink 4- J. a L l -Howeyer+since a" calling subscribers group has access to both groups of line finders, that is, a group in the two upper banks, andia group in the two lower ones andsince, also,

inc finders are allotted indiscriminately from either group by a distributor switch such as 302 or 311,-the link, when assigned,

must know, whether or notthe trip magnet of; its associated link finder shaft 15 to be the locationof the callingli-nelinderfon the wofpairs of banks in the link finder frame and hence controls also the operatingcircuit of-the trip. magnet of the link finder shaft of the assoclated: link. Relay ll? of each ,line, finder :is provided with a pair of left inner contacts one of which is or isnot connected to ground depending upon whether or not the line finder. circuit ofwhich relay @417 is a part. is terminalsended on the two upper or two lowerbanks respectively of the link finderframe.

on the bottom outer contacts of relay The other of the twocontacts is connected to conductor 433 wh1ch is likewise multipled to corresponding contacts of other relays 417 of the line finders cooper- I atmg with one group of links and the com--- mon multiple conductor is carried to the right outer ill'll'lfltLlI'Q of relay 316 of the associated link start circuit. When, therefore, a line finder is taken into use and relay 417 is operated as already described, conductor 433' is or is not grounded depending upon whether the line finder so allotted is associated with a group appearing in the two upper banks or one appearing in the two lower banks. finder appearing in the upper banks, the

ground connected to conductor closes a circuit through the right outer back contacts of relay 316 through cam of the particular link which is in position 3, conductor 340,

winding of relay 500 to battery, operating this relay. On the other handif the assigned line finder belongs to the group appearing in the two lower banks of the link finder, relay 417 is operated but no ground is connected to the left innercontacts of relay 417 and consequently no ground will be present on conductor 3&0 and relay 500 will notoiierate. Relay 500 controls the operation of the trip magnet circuitof the assigned link as more fully described hereinafter.

Returning now to the operation of the allotted link and remembering that sequence switch 509 is in position 3 prior to its being taken in use by a calling line finder and assuming, further, that the allotted line finder belongs in a subgroup appearing in the two vupper banks, then relay 500 operates over the aforetraced circuit and over its top contacts'locks to ground on the bottom front contacts of relay 503 which is already operated over an aforctraced circuit to ground 320 when the line finder is allotted. Relay 503, it will be recalled, operated and closed its top winding over its top inner contacts, right upper and left lower contacts of cam 514:, bottom inner contacts of jack 506 to brush 510. Relay 503 also closed a circuit from ground over its bottom front contacts to conductor 507, supplying thereby a locking ground for relay 500 and also, by this same ground, Operated relay over a circuit previously described and preventing the extension of ground on the contacts of relay 320 over conductor 505 to any other link which may havebeen assignedjust at this time, as already described. Relay 503 then closed an More If it is associated with a line 

